1. Field of the Invention
The present invention relates to semiconductor devices and methods of fabricating the same, and more particularly, to semiconductor devices having line type active regions and methods of fabricating the same.
2. Description of Related Art
As the integration degree of semiconductor memory devices such as DRAM devices continues to increase, the area available to memory devices integrated on a wafer is reduced, and the areas occupied by transistors and capacitors are also reduced according to a predetermined ratio. A basic component of semiconductor memory devices is the memory cell, in which a single bit of information can be stored. The DRAM device comprises a plurality of cells, each having one transistor and one capacitor, and peripheral circuits which can perform read and write operations in order to store information in the cells and retrieve information from the cells.
A conventional DRAM cell array has island type active regions. As the integration degree of the memory device increases, areas of the island type active regions accommodating individual transistors are also reduced. Therefore, although a mask design may have the shape of a rectangle, the active regions actually defined on a substrate have a rounded shape, approximately the shape of a circle due to technical limitations in the photolithography and etching processes. In addition, as areas of interconnections and capacitors connected to the island type active regions become further reduced, misalignment such as over-contact occurs, causing a reduction in device fabrication yield and device reliability. In addition, as the active regions are defined with the island shape, areas occupied by device isolation regions which are required for insulation between the active regions are necessarily relatively large in the substrate, so that there is a limitation in the integration density of the devices.
Therefore, there has been proposed a method of electrically isolating the cells by forming line type active regions, forming device gates and device isolation gates to intersect the line type active regions, and applying a voltage so as to prevent occurrence of current channels from forming under the device isolation gate. However, the method of isolating the devices by using the device isolation gates cannot effectively perform device isolation function in comparison to the method using the island type active regions. In addition, as the integration degree increases, a width of the gate is reduced, so that a device isolation gate function cannot be efficiently performed.